Uh oh...sorry to hear that Chewie's hormones are getting the best of him. Testosterone affects each male rat individually and sometimes they have such an excess of the hormone that they just can't deal. It's a fine balance when it comes to naturally territorial animals and crazy hormones. Hormonal aggression is one of the top unwanted personality traits that breeders work hard to eliminate in their lines, and sometimes when rescuing a rat from a shelter or pet shop, you don't know the genetic history and the potential for hormonal aggression to manifest as the rat reaches adulthood is there.
You'll need to give Chewie an adjustment period after the neuter to allow that over abundance of testosterone to work its way out of his system. An adjustment period will give his brain the time to adjust to the sudden hormonal changes, so he may still be a stinker for a short period before those little testosterone receptors in his brain shake off the last of the male hormones.
Others may suggest a shorter or longer adjustment period but considering that he is waiting on a companion and he will be a lone rat for that period, I'd go with no more than 2-3 weeks.
Having a neutered male and an intact male cohabiting together shouldn't be an issue. The only issues you may run into are when you begin introductions. The intact male may be the aggressor or Chewie may not be very confident and even w/ a neuter, he may instigate a fight...it's really unpredictable when it comes to introducing any rat regardless of the sex or age. I'm hoping that since Chewie's new bro is coming from a breeder that you'll be able to avoid having a rocky experience with intros and the new rattie will be pretty mellow considering his genetics.
Just be prepared to take intros slowly and carefully since both of these guys are older than 6 months and rats are naturally suspicious and defensive towards strange, unknown rats. Even the most difficult intros that take months are well worth the effort when you catch everyone snuggling together!
Be sure to check back once you're ready for intros and folks here can offer guidance and support.